The invention relates to a clutch actuator for actuating a clutch between a drive engine and a transmission of a motor vehicle, in particular a commercial vehicle, including a linearly actuable pin which acts on a release mechanism which is coaxial with respect to a center axis of the clutch.
A clutch actuator of this type is known, for example, from DE 100 14 225 A1. A clutch actuator of this type is usually flanged onto the outside of the transmission housing and has a linearly actuated pin, which is arranged parallel to the center axis of the clutch and is coupled to one end of a disengagement lever which is mounted pivotably within the clutch housing, the other end of the disengagement lever actuating a clutch operator, for example a disengagement bearing, which is coaxial with respect to the clutch center axis. The disengagement lever is loaded with high forces and bending moments, for which reason it has large dimensions and is usually configured as a forging, which in turn causes relatively high manufacturing costs. Moreover, the disengagement lever offers only a low force transmission ratio, with the result that the clutch actuator has to be of correspondingly large dimensions.
DE 44 43 649 A1 discloses electric-motor actuation of a friction disk clutch, which is actuated constantly in the engagement direction by a clutch spring and is disengaged by a thrust ring which acts on the clutch spring. The thrust ring is supported on a housing of a disengagement bearing which can be adjusted by rotation about its axis. A toothing system is arranged on the circumference of the housing, into which toothing system a worm gear engages which is driven by an electronically actuated electric motor. It is disadvantageous here, however, that a relatively large, expensive and heavy electric motor has to be provided for relatively large clutches, as are used in commercial vehicles.
U.S. Pat. No. 2,055,258 A shows a device for actuating a friction clutch, in which device a rotational movement of a shaft is converted via an eccentric pin into a linear movement of a wedge of a wedge mechanism. The linear movement is converted, in turn, into an axial displacement of friction elements of the clutch. This construction is, however, relatively complex.
The present invention is based on developing a clutch actuator of the type mentioned above, in such a way that it is of simple and compact construction and at the same time has a high power density.
According to the invention, a clutch actuator is provided for actuating a clutch between a drive engine and a transmission of a motor vehicle, in particular a commercial vehicle, including a linearly actuable pin which acts on a clutch operator which is coaxial with respect to a center axis of the clutch. The pin is formed by a piston rod of a piston, which is actuated by a pressure medium, of a cylinder-piston unit and is arranged substantially in a plane which is perpendicular with respect to the center axis of the clutch, and is coupled eccentrically to a rotary element of a gear mechanism which converts its rotational movement into a linear movement of the clutch operator.
It is an advantage of the invention that the expensive disengagement lever can be dispensed with by virtue of the fact that the pin is arranged substantially in a plane which is perpendicular with respect to the center axis of the clutch, and is coupled to a rotary element of a gear mechanism which converts its rotational movement into a linear movement of the clutch operator. As the pin, which is present in any case, then replaces the disengagement lever but has to transmit only compressive forces instead of bending moments, it can be dimensioned as previously with a relatively small cross section. The omission of the disengagement lever makes it possible to arrange the clutch actuator, which is flanged onto the outside of the transmission housing of the drive engine in the prior art, at least partially within the housing. As a result, the installation space which is required is reduced advantageously.
Furthermore, substantially greater force transmission ratios can be realized by gear mechanisms which convert rotational movements into linear movements, such as spindle mechanisms or disks having intermeshing ramp-shaped toothing systems, than by the disengagement lever of the prior art. As a consequence, the clutch actuator has to apply lower actuation forces, which in turn makes a smaller clutch actuator possible. Moreover, gear mechanisms of this type have a very small overall size as a rule, which further reduces the required installation space.
In many clutch actuators, the clutch travel is detected by a distance measuring sensor, which measures, for example, the path which is traveled by the pin. On account of the greater force transmission ratio which is made possible by the gear mechanism used within the context of the invention, substantially longer actuating paths for the pin result. As a result, the required resolution of the distance measuring sensor is reduced, which permits the use of a cheaper distance measuring system.
The pin is formed by a piston rod of a piston of a cylinder-piston unit, which is actuated by pressure medium. The pressure medium is a hydraulic fluid or compressed air. The clutch is then actuated by applying pressure to a pressure chamber of the cylinder-piston unit of the clutch actuator or relieving the latter of pressure. A clutch actuator, which is configured in this way, can be used both alone and in combination with an automated change speed gearbox, in which the clutch pedal is omitted.
Advantageous developments and improvements of the invention are described and claimed herein.
In order to realize the eccentric articulation or coupling of the piston rod on the rotary element, an imaginary extension of the piston rod can be spaced apart a little from the center axis of the rotary element.
In the clutch actuators of the prior art, every individual working stroke of the clutch actuator always includes the clutch actuation stroke, which is necessary for the actuation of the clutch and, in addition, a wear tracking stroke to compensate for the clutch wear. This means that the working stroke becomes larger and larger as the wear increases, and the clutch actuator, accordingly, has to be designed for the working stroke which includes the wear tracking stroke corresponding to the overall permissible wear in the most unfavorable case and, in addition, the normal clutch actuation stroke. This gains even more significance if the maximum wear tracking stroke is substantially larger than the clutch actuation stroke in practice, for example in commercial vehicles. As a consequence, the known clutch actuator has a relatively large overall size and is expensive to manufacture.
According to one particularly preferred embodiment of the invention, the initial position of the clutch operator prevailing at the beginning of a clutch actuation can be set as a function of the wear of the clutch by a preceding work stroke of the pin, which work stroke comprises a clutch actuation stroke and a wear tracking stroke. At the same time, the clutch actuator according to the invention is actuated by a control unit in each case separately for the larger work stroke of the pin, which comprises the wear tracking stroke and the clutch actuation stroke and, for a smaller work stroke, which comprises only the clutch actuation stroke. As a consequence, a wear tracking operation also takes place at the same time as the clutch actuation stroke only in some of the work strokes of the clutch actuator, while the initial position of the clutch operator is adjusted in the wear tracking direction. In contrast, only the constantly equally large clutch actuation stroke is carried out in the remaining work strokes. For example, a work stroke with wear tracking is carried out only after a multiplicity of pure clutch actuation strokes, and the next work stroke with wear tracking is carried out in turn only after a multiplicity of pure clutch actuation strokes. As a consequence of this, the proportion of the work stroke which is required for wear tracking in every step of wear tracking is very small compared with the pure clutch actuation stroke, with the result that the work stroke, which is to be made available overall by the clutch actuator, comprises almost completely the pure clutch actuation stroke. As a consequence, the work stroke is substantially shorter than in the prior art, with the result that the clutch actuator can be dimensioned to be smaller and consequently less expensive. Moreover, the pin of the clutch actuator assumes an advantageous dual function, as it is provided firstly for clutch actuation and at the same time for wear tracking.
The control unit is configured, for example, in such a way that, when the detected clutch wear has exceeded a predefined value and a request signal is present for clutch actuation, the control unit triggers in the clutch actuator a work stroke which includes the wear tracking stroke and the clutch actuation stroke. As a result, one criterion is defined for when a work stroke with wear tracking is to take place.
In order to apply pressure to the pressure chamber of the cylinder-piston unit or to relieve the pressure, there are usually electromagnetic valves. In order to make it possible to replace these valves with as low an assembly complexity as possible in the case of a defect in the valves, the valves of the cylinder-piston unit protrude at least partially out of the transmission housing.
Furthermore, a wear tracking device is preferably provided with a spindle drive, it being possible for an axially fixed spindle of the spindle drive to be screwed in the clutch actuation direction in the clutch operator which forms the nut and is held fixedly in terms of rotation, the spindle being coupled rotatably to an actuator of the wear tracking device.
According to one particularly preferable development, the actuator is formed by a toothed disk having a circumferential crown gear, a wear tracking stroke corresponding to at least the tooth pitch of the toothed disk, as viewed in the circumferential direction. The wear travel which has been set can then be detected by counting the wear tracking strokes and can be stored in a readable memory of the control unit, for example in an EEPROM. The current clutch wear can then be read out from the memory at any time and the clutch can be replaced within the context of a preventative maintenance operation when the wear limit has been reached.
The gear mechanism, which converts a rotational movement of the rotary element into a linear movement of the clutch operator, preferably comprises a spindle drive, in which the clutch operator forms the nut and the spindle can be coupled rotationally to the rotary element. The spindle is guided axially fixedly and the clutch operator is guided rotationally fixedly. This type of gear mechanism is very inexpensive on the one hand, and on the other a large range of transmission ratios can be covered, for example by the use of recirculating ball spindle drives.
The spindle and the nut of the spindle drive for actuating the disengagement bearing during a clutch actuation stroke are preferably identical to the spindle and to the nut of the wear tracking device, with the result that these components advantageously perform a dual function. The number of components of the clutch actuator and, as a consequence, also the manufacturing costs are thus reduced.
The rotary element can advantageously be coupled rotationally by a coupling device to the toothed disk, which is connected fixedly in terms of rotation to the spindle of the spindle drive. The coupling device is then configured in such a way that the toothed disk is always coupled fixedly in terms of rotation to the rotary element in a smaller work stroke of the pin, which includes only the clutch actuation stroke, while the coupling device permits a defined relative rotation between the toothed disk and the rotary element in the larger work stroke of the pin, which includes the wear tracking stroke and the clutch actuation stroke, in order to move the initial position of the clutch operator for the following work stroke in a direction which compensates at least partially for the wear of the clutch.
The coupling device includes, for example, at least one coupling element which is guided movably on the rotary element, can engage into toothed intermediate spaces of the crown gear and can be actuated by coming into contact with a stop during the larger work stroke, which includes the wear tracking stroke and the clutch actuation stroke.
According to a further embodiment, the gear mechanism which converts a rotational movement of the rotary element into a linear movement of the clutch operator can have a rotary disk, on which the pin is articulated eccentrically, having a ramp-shaped toothing system which engages in a complementary ramp-shaped toothing system of a further axially displaceable mating disk which is held fixedly in terms of rotation and is coupled to the clutch operator. As a result of this, an extremely simple construction provides for a conversion of the linear pin movement perpendicularly with respect to the center axis of the clutch into a linear movement of the clutch operator in the direction of the center axis and, at the same time, an advantageously high force transmission ratio. In order to minimize wear phenomena and frictional losses, the two toothing systems are roller-mounted relative to one another according to a further advantageous measure, for example by the use of ball bearings.
In this exemplary embodiment, in the larger work stroke of the pin which comprises the wear tracking stroke and the clutch actuation stroke, the toothed disk can be set in rotation such that the initial position of the clutch operator for the following work stroke is moved in a direction which compensates at least partially for the wear of the clutch, and such that, in a smaller work stroke of the pin which comprises only the clutch actuation stroke, the toothed disk cannot be set in rotation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.